Soil Ph and nurtient availability

Mike LarkinDecember 2, 2004

Not all nutients are available at lower or higher Ph levels. For example

Phosphorus (P): Availability is strongly influenced by soil pH. Availability of P is maximized when soil pH is between5.5 and 7.5. Acid soil conditions (especially I copied this from a web site, but understand the basic idea. The P is not available for the plant.

So my question is--- If you have a plant that needs an acid soil, like conifers etc, how does the plant handle the fact that the P is not avaiable?

"If you have a plant that needs an acid soil, like conifers etc, how does the plant handle the fact that the P is not avaiable? "

A very big question ... if the soil had zero Phosphorous available the plant could not survive ... only to the extent it was able to use the mineral in question already stored in it's tissues ( In your example those containing Phosphorous and this ability will vary with different minerals and not enough togrow a large plant )... what is really happening though with availability in most cases is that the availability is not at an optimum level ... so it is more costly for the plant to aquire the mineral in question and even then a deficit may occurr ... the plant is stressed.

How significant the stress is and how much strain ( damage) it may cause depends on the plant and many different environmental factors ...

I must take off ... lunch time ... perhaps someone else can add some more.

"Have conifers, or other plants that grow best in acid soil, adapted in some way to the fact that some of the nutrients are not as avaiable in the acid soil. "

I would suspect they do have such adaptations .. just as our natives have adaptations for high salt soils and high pH ( like salt glands )... off the top of my head I am not up on root adaptations of plants that grow in acid soils.

What is evident from research is that plant systems are highly integrated within themselves and the environment and plants often can not get what they need at luxurious levels so they must optimize in various ways to get the best all around solution ( nutients , light , carbon dioxide assimalation .. transpiration ect ect.. ). There is a vast literature on this subject.

"If we grew acid loving plants in neutral soil, then the nutrients would be more avaiable, but the soil Ph would not be optimal."

Keep in mind as soil pH changes some nutrients may become more available while others less available ... some are not affected at all by pH .. nutrients can also become toxic at certain pH levels .. too much of a good thing.

On a practical side changing soil pH is often not very feasable endeavor ... plant selection is an important factor ...out here we have some ornamentals prone to Iron deficiencies that still do OK with a little extra care.

Mycorrhizae is known to improve the phosphorus uptake of host plants. The hyphae can penetrate the soil beyond the region of phosphorus depletion of the root zone. Mycorrhizae may also be involved in the decomposition of organic sources of P. They may even increase the weathering of P from the soil base material.

Not all conifers prefer an acid pH. Keep in mind that many spruces come from regions where the soil is extremely alkaline. You asked if plants that live from in acid soil have adapted to the lack of availability of certain soil nutrients. Absolutely. Carnivorous plants are a perfect example. The pitcher plant finds an abundant source of nitrogen and other nutrients in the insects it captures.

Have conifers, or other plants that grow best in acid soil, adapted in some way to the fact that some of the nutrients are not as avaiable in the acid soil? Clearly plants in the Ericaceae have found ways of utilizing phosphorus sources that many other plants cannot. It may be related to Mycorrhizae associations or they may find another way to utilize organic sources of N and P that many other plants cannot. The pH alters the availability of elements in certain forms that are useful to most plants. Those elements are still present, so if a plant can find a way to dissociate them, that would give them an advantage. Perhaps some plants are able to change the pH of the soil in the immediate vacinity of the root? I've wondered about this myself but haven't looked into it much.

"Mycorrhizae is known to improve the phosphorus uptake of host plants. The hyphae can penetrate the soil beyond the region of phosphorus depletion of the root zone. Mycorrhizae may also be involved in the decomposition of organic sources of P. They may even increase the weathering of P from the soil base material".

If a small Pine was planted, by nature or man, in soil that was not as acid as needed for best growth, wouldn't the falling needles decomposing over the root system every year have some effect on the soil beneath the tree? And then the pine seeds would more easily take root and eventually a small grove would ensue. josh

We grow 5 species of Pines here in Alkaline soil ... Iron deficiency seems to be the problem mentioned caused by the higher pH.

It's been said that Pine needles can influence soil pH but remember soils can resist changes in pH as well. In any event adding organic mulches to the soil out here is standard for plants that would benafit from lower pH .. since decomposition releases organic acids although the overall effect may not be substansial it is at least moving things in the right direction and maybe can change pH near absorbing roots.

This is why I find plants so interesting. I know a little about Pinus banksiana because I had them growing in my back yard. They are normally found in sandy or other well drained soils, but mine were growing in a heavy clay soil derived from a dolomitic limestone glacial till. From what I could gather from existing literature, the ability of this particular species to grow in soil types like this is related to a mycorrhizae.

I have read, and personal observation in some areas bears this out, that eastern hemlocks rely on rotting wood for seedling production. Apparently the well decomposed remains of fallen trees creates a mound of soil that remains evenly moist throughout the year. If you've ever tried growing hemlock from seed you know that the seedlings can never be allowed to dry out. There might also be something else in this type of "soil" that benefits the seedlings. I have noticed that young hemlocks growing in the woods near me seem to be on slightly raised mounds of earth. I have also seen seedlings growing out of well-rotted wood.

The reason we use terms such as "tolorates acid" or "alkaline loving" plants is precisely their ability to deal with these conditions.

Plants which are acid lovers have found a way to take up only low amounts of nutrients such as boron, copper, iron even under acidic soil pH. E.g. they are quite "wasterful" if you like. If you grow it in alkaline conditions, they can not extract enough from the little which is available and this is why micronutrient deficiencies usually slow in acid loving plants growing in high soil pH. This also explain why they often die from phosphorus poisioning which they used to extract very efficiently. With phosphorous suddenly becoming much more readily available, they overdose on phosphorus.

In similar manner to their acidic loving cousions, Alkaline loving plants have been used to extracting calcium/magnesium/phosphorous quite easily and if growing in acidic soils they will also have difficulty extracting. You may say they are not good enough to do that (have never been challenged to do so). More commonly, however, before alkaline loving plants die from lack of macro nutrients, they will first be "poisioned" by the sudden large availablity of micronutrients (micronutrients are too readily available).

I would add that simply because a plant can tolerate a given set of conditions such as alkaline soil does not mean the plant is adapted or has adaptations to that condition.

Tolerance and adaptations are not the same. An adaptation is a feature that allows an organism to survive and reproduce better in it's natural environment. Tolerance is a plants capability to adjust to less then optimal conditions which could be an adaptation but also may not be an adaptation.

"I have read, and personal observation in some areas bears this out, that eastern hemlocks rely on rotting wood for seedling production"

This is interesting I have read that Giant Saguaro Cactus also requires the debris from certain associate plants as mulch to provide moist conditions for seedling germination and establishment. In addition to cold the lack of these mulch providing plants may provide an additional limitation to the range of this Cactus.

Also the word adaptation has two conotations. An adaptation can be a feature that allows an organism to survive and reproduce better in it's natural environment. Or adatation can refer to the process by which aquires the feature that allows an organism to survive and reproduce better in it's natural environment.

The saguaro's range is also limited by the rain patterns of the Sonoran Desert: winter rains that proceed flowering and the so called summer monsoons that facilitate seed germination.

Plants differ in their ability to take up and utilize nutrients. The plants are adapted through generations of growing in their native habitats to certain conditions.

rhododendron for example, which like a very acid soil, has developped an "inefficient" - or you may call it wastefull - way to taking up micronutrients (metals) and a very effeicient way to taking up phosphorus, calcium, magnesium, potassium, etc. The fact that the uptake of micro nutrients is "inefficient" means that although readily available, it "wastes" a lot and only take up what is truly needed for plant growth.

Therefore, if you plant rhododendron in alkaline soil, the lack of micronutrients combined with it's watefull use of these will surely lead to micronutrient availability.

Compare this to an alkaline plant, lupines for example, which has developped a very effective harvesting mechanism for using micronutrients. IF this plant is planted in acidic soil, it will be poisoned by the excessive metals now available.

At soil pH below 5.2 aluminum becomes much more soluble. Aluminum is toxic to many plants and they will not grow well in very acid soils. Above 5.2, even though there is a lot of aluminum in the soil, it is not in a very soluble form and does not interfere with plant growth.